This proposal will map the changes in the distribution of Na ion, K ion -ATPase and other glycoproteins on the surface of the preimplantation mammalian embryo with the objectives of pinpointing 1. the times and 2. the locations of membrane changes involved in the development of the trophoblast. The specific aims of the research will be: 1. to determine when ATPase and other glycoproteins become localized to the apical and/or basal surfaces of the trophoblast cells using ferritin-antibody and ferritin-lectin labelling techniques in conjunction with electron microscopy, 2. to biochemically characterize the apical and basal glycoproteins by I125 labelling and electrophoretic analysis, 3. to determine if cell-cell contact is required to initiate cell surface and cortical cytoplasmic changes during compaction with micromanipulation technique followed by scanning and transmission electron microscopy, and 4. to study the roles of microvilli and microtubules in cell spreading with specific drug inhibition followed by light and electron microscopic analyses.